Device for coating the outer edge of a substrate during microelectronics manufacturing

ABSTRACT

New baffles and methods of using these baffles are provided. The baffles comprise a body having an edge wall configured to direct the flow of a composition against a substrate (e.g., silicon wafer) edge. The edge wall comprises a vertical surface, a curved sidewall coupled to the vertical surface, and a lip coupled to the curved sidewall. A preferred baffle is annular in shape and formed from a synthetic resinous composition. Even more preferably, the baffle is not formed of a metal. The inventive methods comprise positioning the baffle adjacent a substrate during a spin coating process so that the edge wall causes the composition to cover the edges of the substrate and preferably a portion of the back side of the substrate.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/268,196, filed Nov. 7, 2005, which claims the prioritybenefit of U.S. Provisional Patent Application No. 60/626,034, filedNov. 8, 2004, both of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is broadly concerned with a baffle useful fordirecting a coating composition towards and over the edges of asubstrate during microelectronic fabrication.

2. Description of the Prior Art

Microelectronic devices such as integrated circuits andmicroelectromechanical (MEMs) devices are typically formed by applyinglayers of coatings onto a substrate and forming those layers into theshapes and sizes needed for the particular device design. These layersare typically formed by spin coating a liquid composition onto thesubstrate, however, the coating does not typically flow to and over theedges of the substrate, thus leaving them unprotected. The substratesare subsequently subjected to etching and polishing processes. These arerelatively harsh processes. As a result, the coatings often experiencelift-off problems at their edges, i.e., the edges of the coatings pullaway from the substrate. This leaves the substrate unprotected at itsedges and vulnerable to subsequent processing conditions. The substratewill often become thinner and susceptible to cracking and breaking. Thisresults in a reduction in wafer yield, thus increasing cost.

SUMMARY OF THE INVENTION

The present invention overcomes these problems by broadly providing anovel baffle for affecting the flow of a composition during applicationof the composition to a substrate and directing that flow to and overthe edge, and possibly back side, of the substrate.

In more detail, the baffle preferably comprises a body that is annularin configuration and includes an inner edge wall defining an opening andconfigured to direct the flow of the composition to the substrate edge.The edge wall comprises a vertical surface, a curved sidewall coupledwith the vertical surface, and a lip coupled with the curved sidewall.

In use, the baffle and substrate are positioned so that the substrateedges are adjacent to, but preferably not in contact with, the baffleedge wall. The composition is then applied to the substrate via atypical spin coat process, with the centrifugal forces causing thecomposition to flow to the outer periphery of the substrate, and thustowards the baffle. The baffle edge wall causes the composition to coverthe edges of the substrate. The wafer can then be subjected to furtherprocessing (e.g., baking/curing, etching, further layer application,etc).

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a schematic drawing depicting the problems associated with theprior art processes;

FIG. 2 is a perspective view of a baffle according to the presentinvention;

FIG. 3 is a sectional view taken along line 3-3 of the baffle of FIG. 2;

FIG. 4 is a schematic drawing illustrating a coating process utilizingthe inventive baffle;

FIG. 5 is a Scanning Electron Microscope (SEM) photograph depicting theedge view of a virgin silicon wafer;

FIG. 6 a is an SEM showing the edge of a silicon wafer after beingcoated with a protective material according to a prior art process;

FIG. 6 b is an enlarged view of the edge of FIG. 6 a;

FIG. 7 is an SEM depicting the “knife-edge” obtained after the wafer ofFIG. 6 a was subjecting to a wet etching process;

FIG. 8 a is an SEM illustrating the edge of a silicon wafer after beingcoated with a protective material while using the inventive baffle;

FIG. 8 b is an enlarged view of FIG. 8 a, showing the edge of theprotective coating on the wafer;

FIG. 9 is an SEM showing the edge of the wafer of FIG. 8 a after it wassubjected to a wet etching process;

FIG. 10 is an SEM illustrating the back of a wafer after it was coatedwith a protective material;

FIG. 11 is an SEM of the wafer of FIG. 10 after the wafer was subjectedto a wet etching process;

FIG. 12 is an enlarged view of the SEM of FIG. 11; and

FIG. 13 is an SEM photograph illustrating the back of the wafer of FIGS.9-12 after etching and after the protective coating has been removed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a process according to the prior art. A substrate 10having edge 12 is provided. A protective material 14 is applied to thesubstrate 11 via dispense nozzle 16 and formed into a film 18 via a spincoating process. The substrate 10 is then heated on a hot plate 20 andsubjected to further processing. As shown in FIG. 1, the film 18 doesnot cover edge 12, thus leaving it unprotected during subsequentprocessing steps such as wet etching.

The baffle according to the present overcomes this problem with itsnovel design. Referring to FIGS. 2 and 3, a baffle 22 is provided.Baffle 22 comprises an annular base 24 and support member 26. Annularbase 24 includes upper and lower surfaces 28, 30 and circumferentialouter and inner edges 32, 34, respectively. Upper surface 28 slopesslightly towards surface 30 as it approaches edge 34.

Inner edge or edge wall 34 defines an opening 36. Edge 34 includesvertical surface 38 and a lower lip 40. Vertical surface 38 and outeredge 32 are substantially parallel to one another. Vertical surface 38and lip 40 are joined via a bight or curved sidewall 42. It will beappreciated that lower lip 40 extends beyond vertical surface 38,however, this distance should be limited to allow the composition tocollect within curved sidewall 42, but still allow the composition todrain past the lower lip 40. Thus, the length of “L” should be fromabout 1.5-4 times, and more preferably from about 2-3 times. The lengthof “l,” e where “l” is the shortest distance from the innermost point(i.e., apex) in curved sidewall 42 to a line 44 that extends verticallyfrom vertical surface 38 towards lower surface 30, and “L” is thedistance from line 44 to the end 46 of lower lip 40, as shown in FIG. 3.

Lip 40 comprises an upper lip surface 48 that preferably slopes in adownward direction towards lower surface 30. The angle of slope of upperlip surface 48 is preferably from about 1-15°, and even more preferablyfrom about 2-10°, with a perfectly horizontal line being a slope of 0.

Support member 26 of baffle 22 comprises an upright member 50 and aflange 52, with flange 52 preferably being substantially perpendicularto upright member 50. In a preferred embodiment, flange 52 will compriseat least 2, and preferably at least 3, leveling devices 54. Preferreddevices 54 comprise protrusions 56 extending therefrom, with each ofthese protrusions 56 comprising an opening 58 configured to receive anadjustable fastener such as a set screw (not shown) that can be used toadjust the baffle 22 as necessary. It will be appreciated that the abovespecifications allow the baffle to be sized for the particular processconditions (e.g., substrate size, equipment being used, etc.), makingthe inventive baffle quite versatile.

Baffle 22 can be formed of a number of different materials, dependingupon the equipment, process conditions, etc. to which it will beexposed. However, it is preferred that the baffle 22 be formed of asynthetic resin composition that is resistant to (i.e., will not reactwith or be eroded by) solvents that are typically utilized duringmicroelectronic manufacturing. Such solvents include those selected fromthe group consisting of propylene glycol monomethyl ether acetate,propylene glycol monomethyl ether, ethyl lactate, methyl isoamyl ketone,n-methyl-2-pyrrolidone, and isopropyl alcohol.

It is also preferred that the baffle 22 be formed of a non-metallicmaterial. That is, the material forming baffle 22 would comprise lessthan about 5% by weight, preferably less than about 1% by weight, andmore preferably 0% by weight metal, based upon the total weight of thebaffle taken as 100% by weight.

Particularly preferred materials of which baffle 22 can be formedinclude those selected from the group consisting ofpolytetrafluoroethylene (TEFLON®), polyethylene (preferably highdensity), polypropylene, polyphenylene sulfide, acetals, polyether etherketone (available under the name PEEK from Tangram Technology Ltd.), andmixture of the foregoing.

FIG. 4 illustrates the use of the inventive baffle 22. First, thesubstrate 10 is positioned on a chuck (not shown) within a spin coatingapparatus. Examples of typical substrates 10 include those selected fromthe group consisting of silicon, silicon dioxide, silicon nitride,aluminum gallium arsenide, aluminum indium gallium phosphide, galliumnitride, gallium arsenide, indium gallium phosphide, indium galliumnitride, indium gallium arsenide, aluminum oxide (sapphire), glass,quartz, polycarbonates, polyesters, acrylics, polyurethanes, papers,ceramics, and metals (e.g., copper, aluminum, gold).

The inventive baffle 22 is then placed in the apparatus so that flange52 rests upon a surface of the apparatus (not shown) and so that theedge 12 of the substrate 10 is approximately centered adjacent curvedsidewall 42 within opening 36. The baffle 22 is adjusted as necessaryvia the height-adjusting devices 54 (not shown in FIG. 4) so that thebaffle 22 is level, and the substrate 10 is centered properly. It ispreferred that the baffle is sized so that the distance “D” from theinnermost point or apex in curved sidewall 42 to the substrate edge 12is a distance of from about 0.85-4 mm, and more preferably from about0.85-2 mm. Thus, the substrate and baffle are preferably not in contactwith one another.

After the baffle 22 and substrate 10 are properly positioned, thesubstrate is rotated while dispensing material 14 via dispense nozzle16. Unlike the prior art processes, however, the material 14 willaccumulate in the baffle 22 in the recess created by curved sidewall 42,and the material 14 will be directed towards the substrate edge 12 andeven to the back surface 60 as shown in area 62. Thus, the substrateedge 12 and at least part of the back surface 60 will be covered withthe protective film 18, protecting the substrate 10 from etching,thinning, and other damage during subsequent processing steps. Moreparticularly, when using the inventive baffle, at least about 90%,preferably at least about 95%, and even more preferably about 100% ofthe surface area of the substrate edge 12 will be covered by thecomposition being applied to the substrate.

EXAMPLES

The following examples set forth preferred methods in accordance withthe invention. It is to be understood, however, that these examples areprovided by way of illustration and nothing therein should be taken as alimitation upon the overall scope of the invention.

Example 1 Comparative Example

A prior art process was carried out without using the inventive bafflein order to illustrate the drawbacks of that process.

Virgin silicon wafers have smooth, rounded edges. FIG. 5 is an SEMphotograph depicting such an edge. An etch protective film comprisingProTEK primer and ProTEK B (available from Brewer Science Inc.) was spincoated onto a virgin silicon water using a standard spin coatingprocess. FIG. 6 a shows the etch protective film on the wafer. As shownin FIG. 6 b, the edge was not completely covered. The silicon wafer wasthen subjected to a wet etch process using potassium hydroxide. As shownin FIG. 7, the etch process resulted in a “knife-edge” at the edge ofthe wafer. The etching process resulted in lifting of the film, therebyproviding poor protection to the wafer edge. Such a thin wafer edgepresents significant handling problems as it generally leads to thedevelopment of cracks on the wafer, leading to breakage and a reductionin yield. This problem is even more pronounced in thin-wafer handling.

Example 2 Use of Inventive Baffle

The process described in Example 1 was repeated except that a baffleaccording to the invention, sized according to the wafer size, was used.During spinning, the baffle collected the excess etch protectivematerial and coated it on the edge and back of the wafer. As a result,the etch protective material applied to the top, edge, and under-siderim of the wafer, thus encapsulating the wafer and its edges andpreventing lifting of the film at the wafer edge.

FIG. 8 a shows the etch protective material wrapping around and coveringthe edge of the wafer and continuing to the back of the wafer. FIG. 8 bfurther illustrates that the edge of the etch protective coating is wellfrom the edge on the back side of the wafer.

The wafer with protective coating in place was then subjected to a wetchemical etching process using potassium hydroxide. FIG. 9 depicts thewafer after chemical etching, and the edge of the wafer is intact.

Example 3 Use of Inventive Baffle With Backside Dispense

The process of Example 2 was repeated except that a backside dispensewas added to the spin bowl to create a larger area of protection againstwet chemical etching on the wafer. The wafer was coated with aprotective material as described in Example 2. With the backsidedispense being utilized, the protective material was coated on the backof the wafer from the edge to about 5 mm from the wafer edge. FIG. 10shows the back of the silicon wafer after having been coated in thisexample.

The coated wafer was then subjected to a wet etch process usingpotassium hydroxide. FIGS. 11 and 12 illustrate the wafer after etching.The protective material lifted less than 1 mm from the edge of thecoating. The protective material was then removed from the wafer, andthe SEM photograph of FIG. 13 of the back of the wafer was taken. Theentire outer ring of the wafer was protected from etching and remainedintact.

1. In a baffle for affecting the flow of a composition duringapplication of the composition to a substrate having an edge, theimprovement being that said baffle comprises a body having an edge wallconfigured to direct the flow of the composition to the substrate edge,said edge wall of the body comprising: a vertical surface; a curvedsidewall coupled with said vertical surface; and a lip coupled with saidcurved sidewall, said baffle comprising a synthetic resin composition.2. The baffle of claim 1, wherein said synthetic resin composition isselected from the group consisting of polytetrafluoroethylene,polyethylene, polypropylene polyphenylene sulfide, acetals, polyetherether ketone, and mixture of the foregoing.
 3. The baffle of claim 1,wherein said lip presents upper and lower surfaces, and said uppersurface slopes towards said lower surface along a direction away fromthe curved sidewall.
 4. The baffle of claim 3, wherein said slope is aslope of from about 1-15° from a vertical position.
 5. The baffle ofclaim 1, wherein said baffle comprises less than about 5% by weightmetal, based upon the total weight of the baffle taken as 100% byweight.
 6. The baffle of claim 1, wherein: said curved sidewall has anapex, said sidewall having a thickness “l” defined as the distance fromthe apex to a line taken along the same plane as the vertical surface;and said lip extends away from the apex and presents an end, said liphaving a length “L” defined as the distance from the line taken alongthe vertical surface plane to said lip end, wherein the length “L” isfrom about 1.5-4 times greater than the length “l”.
 7. The baffle ofclaim 1, wherein said body and said edge wall are annular in shape. 8.In a baffle for affecting the flow of a composition during applicationof the composition to a substrate having an edge, the improvement beingthat said baffle comprises a body having an edge wall configured todirect the flow of the composition to the substrate edge, said edge wallof the body comprising: a vertical surface; a curved sidewall coupledwith said vertical surface; and a lip coupled with said curved sidewall,said baffle comprising less than about 5% by weight metal, based uponthe total weight of the baffle taken as 100% by weight.
 9. The baffle ofclaim 8, wherein said baffle comprises about 0% by weight metal, basedupon the total weight of the baffle taken as 100% by weight.
 10. Thebaffle of claim 8, wherein said lip presents upper and lower surfaces,and said upper surface slopes towards said lower surface along adirection away from the curved sidewall.
 11. The baffle of claim 10,wherein said slope is a slope of from about 1-15° from a verticalposition.
 12. The baffle of claim 8, wherein: said curved sidewall hasan apex, said sidewall having a thickness “l” defined as the distancefrom the apex to a line taken along the same plane as the verticalsurface; and said lip extends away from the apex and presents an end,said lip having a length “L” defined as the distance from the line takenalong the vertical surface plane to said lip end, wherein the length “L”is from about 1.5-4 times greater than the length “l.”
 13. The baffle ofclaim 8, wherein said body and said edge wall are annular in shape. 14.In a baffle for affecting the flow of a composition during applicationof the composition to a substrate having an edge, the improvement beingthat said baffle comprises a body having an edge wall configured todirect the flow of the composition to the substrate edge, said edge wallof the body comprising: a vertical surface; a curved sidewall coupledwith said vertical surface and having an apex, said sidewall having athickness “l” defined as the distance from the apex to a line takenalong the same plane as the vertical surface; and a lip coupled withsaid curved sidewall, extending away from the apex, and presenting anend, said lip having a length “L” defined as the distance from the linetaken along the vertical surface plane to said lip end, wherein thelength “L” is from about 1.5-4 times greater than the length “l.” 15.The baffle of claim 14, wherein said lip presents upper and lowersurfaces, and said upper surface slopes towards said lower surface alonga direction away from the curved sidewall.
 16. The baffle of claim 15,wherein said slope is a slope of from about 1-15° from a verticalposition.
 17. The baffle of claim 14, wherein said body and said edgewall are annular in shape.
 18. In a baffle comprising a body having anedge for affecting the flow of a composition during application of thecomposition to a substrate, the improvement being that said bodycomprises an outer margin comprising a leveling device for changing theposition of the baffle relative to the substrate.
 19. The baffle ofclaim 18, wherein said outer margin comprises a flange extending fromsaid body, and said leveling device comprises a protrusion coupled tosaid flange.
 20. The baffle of claim 19, said protrusion includingstructure defining an opening, and said opening being configured toreceive an adjustable fastener.
 21. The combination of: a bafflecomprising a body having an edge wall comprising: a vertical surface; acurved sidewall coupled with said vertical surface; and a lip coupledwith said curved sidewall; and a substrate positioned adjacent saidcurved sidewall but not in contact with said baffle.
 22. The combinationof claim 21, wherein said body and said edge wall are annular in shape.23. The combination of claim 22, said edge wall defining an opening, andsaid substrate being positioned within said opening.
 24. The combinationof claim 21, said baffle comprising a synthetic resin composition. 25.The combination of claim 21, said substrate being a microelectronicsubstrate.
 26. The combination of claim 25, said substrate beingselected from the group consisting of silicon, silicon dioxide, siliconnitride, aluminum gallium arsenide, aluminum indium gallium phosphide,gallium nitride, gallium arsenide, indium gallium phosphide, indiumgallium nitride, indium gallium arsenide, aluminum oxide, glass, quartz,polycarbonates, polyesters, acrylics, polyurethanes, papers, ceramics,and metal substrates.